Immunohistochemical localization and comparison of carboxypeptidases D, E,and Z, alpha-MSH, ACTH, and MIB-1 between human anterior and corticotroph cell "basophil invasion" of the posterior pituitary

Basophil invasion, i.e., invasion of basophilic corticotrophs from the resi dual intermediate lobe into the posterior lobe of the human pituitary gland , is believed to be a physiological phenomenon. This study evaluated the di stribution of CPE, CPD, CPZ, alpha -MSH, ACTH, and Ki-67 immunoreactivity b etween human anterior pituitary and basophil invasion of the neurohypophysi s. Mild to moderate immunoreactivities for CPE and CPZ were distributed rel atively uniformly in the majority of the anterior pituitary cells and basop hil invasion. In contrast, only corticotrophs exhibited intense CPD immunor eactivity. Basophil invasion showed similar immunoreactivities for alpha -M SH, ACTH, CPE, and CPZ as corticotrophs in the anterior pituitary, except f or CPD, which was detected much less frequently. In the posterior lobe, CPE , CPD, and CPZ were present within the Herring bodies. Although no MIB-1 im munoreactivity was identified in anterior pituitary cells, limited MIB-1 la beling was detected in basophil invasion in five of ten cases. Highly selec tive expression of CPD in corticotrophs suggests that CPD plays a particula rly important role in prohormone (POMC) processing in corticotrophs, with m inimal or no significant roles in non-corticotrophs. Evidence that corticot rophs in basophil invasion are undergoing proliferation and are also phenot ypically different from their counterpart in the anterior pituitary has fur ther raised the possibility of some neoplastic potential.